uni'wissen 01-2012_ENG

neutral, meaning that there are exactly the same amount of charges from cations and anions. A well-known example is table salt, whose chemical name is “sodium chloride” and which is com­ posed of equal parts of negatively charged chloride anions and positively charged sodium cations. In his habilitation thesis, Krossing ­created an entirely new kind of anion whose ­purpose consists solely in stabilizing cations with unusual properties. It is precisely these anions that enable a battery to be used after being stored in an oven. Krossing has since created new ions again and again – and they often prove to be very useful. “This is fundamental research, terra incognita. I was not born to improve lithium ion batteries.” But he’s ended up doing it anyway. “The scientific approach is to develop ­fundamentally new substances that are better” more energy can be stored in a battery of the same weight with new electrode materials. There are several ways to produce salts that exhibit the desired behavior. One possibility is to mix addi­ tional additives into the solutions. They can pre­ vent undesirable reactions by blocking highly reactive constituents of the electrolytes. This method will certainly be technically relevant, ­believes Krossing, but he doesn’t think much of it from a scientific perspective. “It’s something I would describe as typical alchemy. We add something to it, don’t really know what will ­happen, and hope that it makes it better. The ­scientific approach is to develop fundamentally new substances that are better.” New Ions Are Often Useful Krossing began his search for new substances 15 years ago in his habilitation thesis, in which he also dealt with salts. A salt is composed of cations and anions, or in other words positively and negatively charged ions. It is electrically A lithium-ion battery is made up of several cells that are only several millimeters thick. In most cases the cells are stacked up in blocks or rolled up in cylinders. The cell of a lithium-ion battery is composed essentially of three components: two metal plates with electrodes attached to them and a plastic film, the separator. One of the elec- trodes consists of a copper plate covered with a coating of graphite and contains many elec- trons. It is thus negatively charged and forms the anode, the negative pole. When the battery is full, the graphite coating also contains the lithium atoms. The separator separates the ­anode from the other metal plate, the cathode – like a thin sandwich with a piece of lettuce ­between two slices of bread. The separator is soaked in an electrolyte, a liquid that conducts the positively charged lithium ions. The cath- ode, the positive pole, is composed of an ­aluminum plate covered with a coating of, for example, lithium cobalt oxide. The cobalt oxide contains many positive cobalt atoms that can absorb electrons. The cathode is thus positively charged. electron lithium atom cobalt atom positively charged lithium ion negatively charged coablt ion aluminum plate (lithium) cobalt oxide coating separator with electolyte (lithium) graphite coating copper plate flowofcurrent cathode separator with electolyte anode Design and Functioning of a Lithium-Ion Battery Diagram: Klaas I. II. 34